AB Initio Geometries for C 2n+1H, C 2n+1H +, and C 2n+1H 2 Species for N = 1,2,3

Ab initio geometries are reported for C2n+1H, C2n+1H+, and various C2n+1H2 species (n = 1, 2, 3). Different planar conformations of the C2n+1H2 molecules are examined, including quasi-linear chains, carbenes based on a three-membered ring with acetylenic side chains, and (H2C)C2n species related to vinylidenecarbene. Excited electronic states of linear HC7H are also considered briefly. For the early members of each series, comparison is made with spectroscopic and astronomical data.